SPECIAL Condensed Matter Seminar - Ben Feldman, Harvard University - "Spin and Valley Influence on the Fractional Quantum Hall Effect in Suspended Gra
Graphene has recently attracted considerable interest because the fourfold spin and valley degeneracy of its charge carriers enables the formation of a rich variety of correlated states at high magnetic field. In this talk, I will discuss electronic compressibility measurements of suspended graphene in the quantum Hall regime. Our measurements reveal a multitude of fractional quantum Hall (FQH) states that follow the standard composite fermion sequence between ? = 0 and 1, but occur only at even-numerator fractions between ? = 1 and 2, suggesting that an underlying symmetry remains. In addition, we observe a series of phase transitions in the FQH states between ? = 0 and 1, which indicate abrupt changes in their underlying order and are marked by a narrow region of negative compressibility that cuts across each FQH state. I will discuss how these results provide insight into the interplay between electron-electron interactions and the spin and valley symmetries of graphene.
B. E. Feldman, B. Krauss, J. H. Smet, A. Yacoby. Science 337, 1196-1199 (2012).
Location: Jadwin A06
Date/Time: 12/21/12 at 1:30 pm - 12/21/12 at 2:30 pm
Category: Condensed Matter Seminar